Brake yokes for disk brakes are usually fixed asymmetrically on the steering knuckle relative to the swing axis of the knuckle, e.g. at the "rear edge" of the disk. The reason for this is there is often no space above the disk in order to mount the brake yoke directly above the axis of rotation of the knuckle. The disadvantage of an asymmetric placement is not significant for lighter brakes, e.g. disk brakes for passenger cars, but the heavier the vehicle is, the heavier the entire brake equipment will be and the heavier the brake yoke will be. In the heaviest class of trucks the brake yokes will be so heavy that placement of a brake yoke at the rear edge of the brake disk for example would involve significant problems with installation and service, since the yoke must be held up while its screws are inserted into the mounting flanges on the steering knuckle. In the heavier class of vehicles, the king pin is traditionally mounted in an upper thrust bearing which is built-up vertically and limits the space so that the brake yoke cannot be given the ideal placement.